To determine the area if the circle, you must know the diameter or the radius of a circle.
If you know the radius of a circle, use this as your formula. Remember: Pi (the greek symbol thingy) is equal to 3.1415. (A is equal to area of the circle and r represents the radius)

If you know the diameter, just divide the diameter to get the radius then use the same equation.
Oop- I’ll pass on telling you everything about me :/
The distance between two cities is
75
k
m
s
.
Explanation:
As a road of
4
c
m
.
on road map indicates a road of length equal to
30
k
m
.
Each
c
m
.
on map indicates
30
4
=
7.5
k
m
s
.
Hence a distance of
10
c
m
.
between two cities on the map indicates
7.5
×
10
=
75
k
m
s